The use of the term ADSL herein is intended to include other forms of DSL signals which are available to one skilled in the art including HDSL, SDSL and VHDSL signals. Also the various forms of ADSL signals can be used such as DMT, QAM or CAP analog format.
The following U.S. patent references have been noted in a search:                U.S. Pat. No. 5,303,229 (Withers et al.) issued 12 Apr. 1994 entitled Optical Network Unit.        U.S. Pat. No. 5,408,260 (Arnon) issued 18 Apr. 1995 entitled Customer premises ADSL signal distribution arrangement.        U.S. Pat. No. 5,767,895 (Yashiro and Sasada) issued 16 Jun. 1998 entitled CATV Telephone System.        U.S. Pat. No. 4,891,694 (Way) issued 2 Jan. 1990 entitled Fiber optic cable television distribution system.        U.S. Pat. No. 5,917,624 (Wagner) issued 29 Jun. 1999 entitled Method and system for applying fiber to the curb architecture using a broadband gateway at service locations, including homes.        U.S. Pat. No. 5,940,738 (Rao) issued 17 Aug. 1999 entitled Video pedestal network.        
With the widespread utilization of the Internet, it has been recognized that there is a demand for various forms of information to be communicated to and from customer premises such as residences. This information includes, in particular telephone service, security and metering services, Internet access and digital video-on-demand services. Internet access and specifically video-on-demand require very high data rates.
Optical fiber networks have the capability of meeting this demand, but do not generally extend to residential customer premises. Telephone subscriber lines extend to residential customer premises but have insufficient bandwidth to carry video signals until the recent development of digital video and DSL (digital subscriber line) technology.
Two technologies, namely cable TV modems, and ADSL (asymmetric digital subscriber line) systems, have been developed for delivering Internet services and bi-directional communications services to customer premises. Both technologies make use of existing wiring to the subscriber location and existing wiring within the customer premises and require, at most, minimal rewiring. Both technologies continue to support existing customer equipment and services.
ADSL typically provides a high data rate channel for transmission in a downstream direction from a telephone CO (central office) to a subscriber, a somewhat lower data rate channel for upstream transmission in addition to POTS (plain old telephone service), via a two-wire telephone subscriber line. Thus this technology can simultaneously communicate Internet data at as well as telephone signals bi-directionally, over a single telephone subscriber line which is referred to as an ADSL loop. ADSL technology, for example the type using multi-carrier modulation, makes it possible to send data at bit rates in excess of 6 Mb/s downstream on telephone subscriber lines.
The principles of multi-carrier modulation are described for example in “Multi-carrier Modulation For Data Transmission: An Idea Whose Time Has Come” by John A. C. Bingham, IEEE Communications Magazine, Vol. 28, No. 5, pages 5-14, May 1990.
A significant problem in the widespread adoption of ADSL technology is the limited range of transmission. Practical limitations are 4 km from the CO for 1.5 Mb/s service and 2 km from the CO for 6 MB/s service. The telephone operating companies are unable to offer ADSL to many of their customers since the serving radius of each central office exchange is typically up to 5.5 km.
One solution to this problem is to shorten the ADSL loop by providing remote extensions to the telephone central office known as remote line units or RAM (remote access modules). Within these units, is provided a DSLAM (digital subscriber access multiplexer) that includes the ADSL modem that is normally located at the CO. The DSLAM digitally multiplexes the data from several ADSL loops and provides and interface to a high-speed digital channel connecting to the CO and typically implemented with SONET transmission on optical fiber.
Unfortunately, the RAM contains relatively bulky equipment that requires power and environmental control. The required enclosure is costly since it must be sized for future service growth and this cost is excessive when the RAM serves only a small number of ADSL customers. Furthermore, the extension of CO equipment into remote access modules requires the deployment of highly skilled service personnel who were previously required only in the CO.